With the advance of techniques in recent industrial and manufacturing fields and the rise of interest in environmental problem, it is strongly demanded to develop metallic materials having high strength and ductility at higher temperatures, particularly a high temperature zone of not lower than 1000° C.
Incidentally, high-temperature materials used from the old time were mainly Ni-based, Cr-based and Co-based alloys. For example, JP-A-55-154542 proposes Ni-based alloy comprising Cr: 20˜35 wt %, Si: 1˜8 wt % and C: 1.7˜3.5 wt % and forming M7C3 type carbide, and also JP-A-61-7145 proposes Ni—Co—Cr based alloy comprising Ni: 20˜47 wt %, Co: 6˜35 wt %, Cr: 18˜36 wt %, C: 0.6˜2.5 wt % and Si: 0.5˜2.5 wt %. However, all of these alloys could be practically used up to only a temperature of about 500° C. And also, these alloys containing a greater amount of Ni or Co have many problems that the cost of the material itself is very expensive and the thermal expansion coefficient is high.
A Cr-based alloy is hopeful as a high-temperature material being cheaper than Ni- or Co-based alloy and small in the thermal expansion coefficient. For example, JP-A-11-80902 proposes a high-Cr alloy containing C: 0.5˜1.5 wt %, Si: 1.0˜4.0 wt %, Mn: 0.5˜2.0 wt % and Cr: 35˜60 wt % and enhancing a resistance to erosion and corrosion at a higher temperature. However, even in this high-Cr alloy, it is difficult to obtain a sufficient strength at a high temperature zone, particularly above 1000° C. In order to further increase the strength of such a Cr-based alloy, it is required to more increase the Cr amount. In the conventional technique, however, when the Cr amount is not less than 60 mass %, the ductility is substantially lost, so that there is a problem that the working after the production is impossible. Therefore, the alloy containing Cr of not less than 60 mass % has been not yet put into practical use.
As mentioned above, practical materials having a sufficient strength at the high temperature and a good workability (ductility) is not existent in spite of a situation that it is more increased to demand materials durable to use under a super-high temperature environment.
It is, therefore, an object of the invention to solve the above problems of the conventional technique and to provide Cr-based alloys having an excellent strength-ductility balance, which has never been attained in the conventional alloy, at a high temperature above 1000° C., particularly a high temperature above 1050° C.